/**
 * 141. 环形链表
 */
public class Solution_141 {
    /**
     * 快慢指针
     * <p>
     * 时间复杂度：O(N)
     * <p>
     * 空间复杂度：O(1)
     */
    public boolean hasCycle(ListNode head) {
        if (head == null || head.next == null) {
            return false;
        }
        ListNode slow = head, fast = head.next;
        while (slow != fast) {
            if (fast == null || fast.next == null) {
                return false;
            }
            slow = slow.next;
            fast = fast.next.next;
        }
        return true;
    }

    public static void main(String[] args) {

    }
}
